1. Field of the Invention
This invention relates in general to certain new and useful improvements in automatic swimming pool cover system and, more particularly, to a cover system using a hydraulic drive for slatted buoyant type pool covers.
2. Brief Description of Related Art
Pool covers are used on many swimming pools. They save energy, keep the pool clean, minimize chemical use and provide desirable safety features. In fact, in windy locations, a pool cover is essential for maintaining pool water at comfortable temperatures at a reasonable expense.
The types of commercially available pool covering systems and those which have been proposed include free floating covers, tie down/stretched covers and track anchored floating covers. Mechanisms for retracting such covers back and forth across a pool include purely manual devices such as the xe2x80x9cRocky""sxe2x80x9d roller manufactured B. C. Leisure Ltd. 113-1305 Welch Street North Vancouver B.C. Canada V7P 1B3; semi-automatic systems (see U.S. Pat. No. 4,351,072) and automatic systems, which are usually electrically or hydraulically powered. (See U.S. Pat. Nos. 2,754,899; 2,958,083; 3,019,450; 3,050,743; 3,613,126; 3,982,286; 4,939,798 and 5,327,590).
Automatic swimming pool cover systems can include a flexible vinyl fabric sized so that most of it floats on the surface of the pool water. The pool water acts as a low friction surface significantly reducing the amount of force required to move the cover across the pool. The front edge of the cover is secured to a rigid boom spanning the width of the pool for holding the front edge of the cover above the water as it is drawn back and forth across the pool.
To draw the cover across the pool, a cable, typically a Dacron line, is incorporated into and forms a beaded tape which is sewn or attached to the side edges of the pool cover. The beaded tape in turn is captured and slides within a xe2x80x9cCxe2x80x9d channel of an extruded aluminum track. The track is secured either to the pool deck or to the underside of an overhanging coping along the sides of the swimming pool. The cables extending from the beaded tape sections of the cover are trained around pulleys at the distal ends of the tracks and return in a parallel xe2x80x9cCxe2x80x9d channel to the drive mechanism where they wind around cable take-up reels.
To uncover the pool, the drive mechanism rotates a cover drum mounted at one end of the pool winding the pool cover around its periphery and unwinding the cables from around the take-up reels. To cover the pool the drive mechanism rotatably drives the cable take-up reels, winding up the cables to pull the cover across the pool while unwinding the cover from around the cover drum.
The present applicant recognized the problems inherent in the use of an electric drive system for operating pool covers. Aside from the numerous safety factors, the electric motors had to be completely insulated from the water environment. Nevertheless, many pool cover drives are located in a subterranean environment. Consequently, the overall costs of construction and costs of installation were considerable. Notwithstanding, even rain water and ground water tended to collect in subterranean compartments housing the electric motors and their associated electrical components. In fact, it has been recognized that at least fifty percent of the failures of most automatic pool cover systems is due to the inherent problem of water damage.
In order to overcome this problem, the present applicant had proposed and provided, as hereinafter described, pool cover systems which rely totally upon a hydraulic drive located at or near the swimming pool. An electric drive could be provided to operate a pump for pumping the hydraulic fluid. However, an electric drive and the pump could be located at a remote location and even housed in a building or the like.
In U.S. Pat. No. 5,184,357 issued Feb. 9, 1993, the present applicant describes automatic swimming pool cover systems wherein a first hydraulic drive provides torque for resisting cover drum rotation during cover extension and for rotating the cover drum for cover retraction. A separate and second hydraulic drive provides torque for rotating the cable reels for cover extension and for resisting cable reel rotation during cover retraction. In this latter U.S. Pat. No. 5,184,357, the desirability of having positive stops located at the respective ends of the pool is taught. These positive stops will stop movement of the rigid leading edge carrying the pool cover by increasing tension load on the cover and cables sufficiently for counter-balancing the torque of the particular driving hydraulic motor which is rotating either the cable reels or cover drum. These mechanisms need only be able to mechanically withstand the differential load of the driving hydraulic motor which rotates the cover drum and the opposing tension load imposed by the pumping hydraulic motor resisting rotation of the cover drum.
In under track systems (where the track is fastened to the underside of overhanging copings), the copings or walls at the respective ends of the pool can function as inherent stops arresting cover extension or retraction, provided however, that the rigid leading edge appropriately engages the coping or walls. Also, return pulleys at the distal ends of the respective tracks which carry the returning cables to the take-up reels, provide inherent positive stops for arresting extension of the cover. The pulley housings do not have xe2x80x9cCxe2x80x9d channels and hence will stop the sliders sliding within the xe2x80x9cCxe2x80x9d channels supporting the rigid leading edge carrying the cover across the pool. [See U.S. Pat. No. 4,939,798 issued Jul. 10, 1990 to applicant, Harry J. Last, entitled: xe2x80x9cLEADING EDGE AND TRACK SLIDER SYSTEM FOR AN AUTOMATIC SWIMMING POLL COVERxe2x80x9d and U.S. Pat. No. 4,466,144 issued Aug. 21, 1984 to Joe H. Lamb entitled: xe2x80x9cPULLEY ASSEMBLY FOR SWIMMING POOL COVERxe2x80x9d].
Automatic pool cover systems utilizing interconnected rigid buoyant slats which roll up on a submerged or elevated drum as described by U.S. Pat. No. 3,613,126, to R. Granderath, are popular in Europe. These pool cover systems utilize passive forces arising from buoyancy or gravity for propelling, the cover to extend the cover across a pool. With either buoyancy or gravity, there must be some mechanism to prevent a retracted cover from unwinding responsive to the passive force. Such passive force systems also have a disadvantage in that the passive force must be overcome during retraction. Granderath suggests a worm gear drive mechanism for winding the cover and preventing cover drum rotation when not powered. The slats for these are further described in U.S. Pat. No. 4,577,352, to Gautheron.
U.S. Pat. No. 4,411,031 to Stolar describes a system similar to Granderath where instead of rigid hinged buoyant slats, various floating sheet materials such as a polyethylene polybubble, or a laminate of vinyl sheeting and foamed substrate, are floated on the surface of the water. The propulsion of the cover across the pool is reliant on buoyant and gravitational forces much like the system in the Granderath patent.
Pool covers which employ floating slats or like materials, and which use buoyant forces to propel the cover across the pool, necessarily wind the cover onto a roller drum which is positioned below the water surface. When the cover is fully retracted from the swimming pool surface and fully wound onto the cover drum, the upper extremity of the complete cover and drum are at least two inches below the surface of the water cover in the pool. In some cases, the cover and drum are located in a separate water filled niche next to the pool. In other instances the cover and drum may be located near the bottom of the pool, or in a special hidden compartment underneath the pool floor to aesthetically hide the cover and roller drum, but also so that the mechanism does not interfere with swimmers.
Buoyant covers, which rely on buoyant or gravitational force to propel the cover across the pool, need to move at a low linear speed, and accordingly a low drum rotational speed, so as to prevent buckling of the cover as it moves across the water surface. A low rotational velocity is also necessary to prevent excess unwinding of the cover still wound onto the drum. In other words, there is a need to balance the resistive friction forces of the cover moving across the water surface against the upward buoyant forces inherent from the buoyant slats or sheeting material or the downward gravity forces where the roller is positioned above the water surface, as the fabric unwinds from the roller drum. The aforesaid Stolar patent recommends a rotational unwinding speed of the cover drum at 3.75 revolutions per minute for covers up to a 40 foot length.
The buoyant upward force resulting from the buoyance of the slats may be determined by taking the area of the cover freely submerged below the water surface, which is derived by multiplying the width of the cover by the amount of cover unwound from the cover drum, from the vertical distance as measured from the center of the diameter of the cover drum to the water surface, and multiplying this by the per square foot buoyant force of the cover material.
In the case of a cover where the drum is located at the pool bottom, the resultant buoyant force may be substantially in excess of the resistive forces. As a result, the roller drum may require a braking force to be applied in the unwinding direction to prevent the cover from unduly accelerating and also for the cover to maintain a cessation of movement at the end of designated travel without creeping, after the cover is at rest. Slats as described by Granderath and Gautheron are generally approximately 13 to 15 mm in thickness. Consequently, a pool cover about 40 feet in length when fully wound onto the cover drum will have a two foot diameter or more.
Most buoyant covers employ a drive system which incorporates a worm gear reducer in the drive train as taught by Granderath. Worm gear reducers generally of the single reduction type usually have a self-locking ability to prevent back driving of the output shaft, and thereby provide a controlled braking force against the buoyant forces tending to unwind the cover from the cover drum. It should be understood that in the case of covers mounted in the pool bottom and in particular, the combination of buoyant upward force and the resultant lever or moment arm from the cover drum diametrical buildup can result in high torque requirements on the motor drive system, adding considerable expense.
Automatic covers of the buoyant type described above typically locate the reducer and electric drive motor exterior the pool wall. The drive shaft of the cover drum passes through an orifice or opening in the pool side wall and incorporates a bearing and several seals and gaskets to prevent pool water from leaking or seeping from the pool around the drive shaft. Considerable expertise and skill is required to prepare and locate the bearing seal arrangement. Furthermore, a separate excavation and structure of sufficient size to house the drum shaft drive mechanism and to facilitate service is required next to the pool wall. In addition to the extra cost associated with the seals and water tight structure it is also very important to prevent rainwater or groundwater from accumulating or seeping into this structure and cause the electric motor and controls from being flooded and damaged. As with the American cable type automatic cover systems, it has been the experience with the European slat type cover systems, that as high as fifty percent of all automatic cover failure is attributable to moisture damage of the electrical drive and control system.
An alternative practice to the shaft-through-the-wall systems is the inclusion of the electric motor inside the cover drum. Typically the motor, for reasons of space limitations, must be coupled with a planetary gear arrangement to be able to substantially reduce the rotational speed required for these covers. Since planetary gears have no braking capability and will back drive, a friction brake must be incorporated inside of the drum, with adequate braking capability, adding to the expense. These arrangements are sold as waterproof systems, but there is little experience as to the durability and life of the seals of these systems and the manufacturers warranties are typically one to two years in duration. In the case of leakage, damage and the replacement labor cost of these systems is expected to be extensive.
Another concern and disadvantage of electrically powered cover systems is the risk of electrical shock hazard. In many U.S. jurisdictions there are strict requirements for bonding and location of the electrical motors near the pool, and in many parts of Europe voltages in excess of 40 volts are not allowed within ten feet of the pool water surface. In the case of systems where the electric drive motor is in the tube there will also be a shock hazard when the enclosure leaks and floods the motor. A problem with low voltages is that the current carrying capacity is low and therefore for long distances away from the pool the cable thickness requirements will be high, expensive and impractical.
Covers using a flexible membrane and side tracks which are pulled open and closed with a cable mechanism, are generally faster, with a cycle time of 30 to 45 seconds. For safety reasons these systems employ a momentary contact switch which the operator must hold and operate for the full cycle of cover travel. Since the primary reason of these safety covers is to prevent entry into the pool, the cover will also trap the swimmer if caught beneath a closed cover. Consequently safety regulations generally mandate the momentary switch to force the cover operator to stay at the control switch while the cover is moving. When the cover reaches the end of travel, the operator simply releases the switch and the cover stops. Because it is often difficult for the operator to precisely see when to stop the cover movement, various forms of electric limit switches and sensors are used to precisely stop the cover automatically.
On cable and side track type of safety covers, coupling of the electric drive gear motor to the cover drive drum and the cable reel is usually by means of a clutch as described in various patents by Lamb and McDonald. This means that rotary revolution counting limit switches, such as described in U.S. Pat. No. 3,718,215, coupled to the gear motor shaft, are usually inaccurate and unreliable. Consequently sensor type limit switches employing the attachment of sensors or magnets to the cover fabric are often used. Also extensive use of electrical control wires is necessary from the sensors to the control switch. Because covers stretch, accumulate dirt and debris, electric control wires snag and break. Also over time sensors dislodge. As a result this type of limit switch is often very unreliable.
A more reliable type of means of stopping the cover at the end of travel is described in U.S. Pat. No. 5,184,357. In this case, with the hydraulically powered pool covers, hydraulic pressure relief valves are often used to stop the cover automatically as the leading edge slider reaches an end of travel. A further patent by the applicant provides a split stop, in which the leading edge slider, sliding in the cover track extrusion, is stopped at the end position by the track end pulley bracket and at the other end by the track split stop. Another means of stopping the cover is described by McDonald using a separate cabling system and electric limit switches activated by stops attached to the cable. A further method is described in U.S. Pat. No. 5,920,922 where the low stretch pulling cable with stopping device attached is used to limit travel of the cover.
Slat type or other buoyant covers which rely on buoyant or gravitational force may take as long as three minutes to cover the pool. Since these covers are generally not classified as safety covers and are generally not secured to the sides of the pool, they can usually be lifted upward to allow a swimmer to get out from under the cover. These covers usually use a latching type of switch which will keep the cover running in one direction and which does not require the operator to stay with the control. The latching type of control however, must have a means of stopping the cover automatically at the end of travel to prevent damage to the system.
As with the cable type pool covers, slat covers will sometimes use sensor type of limit switches and generally experience the same problems with the environment as described above. Since the cover drum is generally directly coupled to the motor drive shaft, rotary limit switch devices as described in U.S. Pat. No. 3,718,215 are reasonably effective. A more recent means is the use of electrical rotary encoders to count rotations of the drive shaft and send an electrical signal to the control system or motor drive. As with the electric drive motors it is important to keep moisture away from these controls to keep them functioning reliably. As described above, this is typically a problem in a swimming pool environment.
Mechanisms for controlling movement of slat type members and other screw drive members and, particularly, to provide limit stops have also been widely used in the aircraft industry. However, these devices are concerned primarily with high speed operation and low torque operation. Exemplary is U.S. Pat. No. 4,930,611 to Grimm and U.S. Pat. No. 4,838,403 to Layer.
A desirable solution for the buoyant slat type, buoyant membrane or even the gravity type of cover, would be to use a hydraulic motor drive system to move the pool cover drum and thereby alleviate the moisture problems, flooding and electrical shock hazard associated with electric pool cover drive systems. The advantage of hydraulic systems is that the power pack pump system can be placed some safe distance away from the pool and in a covered building area. Only two hydraulic lines are required to power the cover system. Little use has been made of hydraulic motors in the buoyant type of cover to date because of the following problems.
One problem with the slat cover, is that there is a constant buoyant force or a gravity force on the cover in the covering direction. One solution that is typically used in similar hydraulic applications, where the hydraulic motor is subject to over-running, is to provide for a counterbalance hydraulic valve or alternatively a brake valve on the output or exhaust port of the hydraulic motor. These counterbalance hydraulic valves include normally closed valves which are opened only when a preset pilot pressure is reached. This pilot pressure source is typically from the outlet pressure of the motor. Hence the motor will not turn until there is enough resistance or braking built up before the valve opens and allows fluid to flow out of the outlet port of the motor and the shaft to turn. This braking effect is maintained throughout the cycle. A brake valve is similar in operation of the pilot valve, but incorporates a second pilot line and is a complicated valve with additional benefits.
Although these brake valves and pilot valves can act as forms of check valves, they will not maintain a motor in a locked condition. This is because unlike a direct brake on a drive shaft, there is an indirect fluid connection. Although the hydraulic motor can prevent rotation better than electric motors by blocking fluid flow on the inlet and outlet ports, there is still enough internal leakage in the motor to cause some creep of the motor shaft when subjected to constant load at rest, such as the torque on the shaft from the buoyant force or gravitational force of a floating pool cover. Slight movement of the motor shaft may occur over time with the shaft under buoyant torque at rest, and consequent movement of the cover. Consequently for applications such as cable winches, positive braking to the output motor shaft must be applied to maintain a safe locked condition. As a result, either a more expensive hydraulic brake motor with additional control systems must be used, or the motor must be coupled with an additional cost worm gear reducer to provide braking, as used with the electric drive motors.
Unlike electric motors, where a gear box with a high gear reduction is necessary to develop the high torque and low shaft speed at the cover drum drive shaft, High Torque Low Speed (LSHT) hydraulic motors can easily run at 4-5 revolutions per minute and at high torque. Adding a worm gear reducer, for braking only, can add considerably to the cost of the drive system. Furthermore, for the reducer to act as a brake it must also possess high internal frictional resistance and must be inefficient. A practical gear ratio of such a worm gear reducer is 20:1. This means that the hydraulic motor must be made to run 20 times faster than if it were directly connected to the drive shaft. This further means that the pump must also put out a substantially higher volume of fluid, which generally increases the cost of the power pack.
A gear reducer in combination with a hydraulic motor actually functions as a direct drive component. Moreover, it becomes a rather costly component to serve as a brake when, indeed, it is not highly efficient for providing braking power. Inasmuch as the gear reducer must be in the gear train, the size of this gear reducer must conform to the torque requirements. Where the torque requirements are high, the size of the gear reducer must be large. Thus, the gear reducer can become a very costly component and merely function as a brake. Consequently, use of the reducer is highly inefficient.
Hydraulic motor systems can easily be fitted with electric rotary limit switches or rotary encoders as described above. These systems can be directly coupled to the drive shaft because the cover is directly coupled. This however requires running electrical control cabling with inherent shock hazard at the pool. Also moisture problems as described above will negate the advantage and reliability of using the hydraulic drive motor. Since there is not a cable pulling the cover to a closed position, the cover cannot be used as a positive stopping means to activate a hydraulic pressure relief valve.
Various types of travel limiting devices are described in a number of U.S. Patents. The aforesaid U.S. Pat. No. 4,838,403 to Layer. In effect, Layer is using a snubber valve to achieve an over-travel stop activated control system. The present invention employs a valve to shut off fluid flow. In effect, fluid flow is blocked to trigger a pressure switch and thereby actuate a latching relay. In contrast, the system in the Layer patent relies upon the braking of a motor from an opposite direction.
Another travel limiting device is described in U.S. Pat. No. 4,064,981 by House and Pierik. This patent describes a shock absorbing feature using a traveling nut on a threaded shaft device to limit the revolutions of a drive shaft on airplane flap actuators. This device is used as a backup in case of failure of the electrical limit systems. The device described is designed specifically to take high speed high torque loads. This device is also complex in construction and uses a two part traveling nut with a pair of concentric jack screws to prevent jamming of this high speed high torque device. In effect, this mechanism is designed for aircraft safety.
The present invention provides for a floating pool cover drive system and cover travel limiting system which overcomes the drawbacks associated with prior floating pool cover systems, while obtaining additional advantages of safety, reliability, lower cost and easier installation.
One object of this invention is therefore to provide a means to control the flow of fluid under pressure to the hydraulic motor to limit the travel of the cover. Another object is to enable using a hydraulic motor to drive the cover system without the use of a worm gear reducer as an unwinding braking force.
In order to avoid and overcome the above problems, the present invention provides for a very simple floating cover drive system which overcomes many of the drawbacks with prior floating cover drive systems while obtaining additional advantages and benefits including lower cost, lower construction and installations costs as well as significantly improving the reliability and also the appearance of such systems. This system is also applicable to both hydraulic and electrical cover drives.
This invention possesses many other advantages and has other purposes which may be made more clearly apparent from a consideration of the forms in which it may be embodied. These forms are shown in the drawings forming a part of and accompanying the present specification. They are also described in more detail in the following detailed of the description of the invention. However, it is to be understood that this following detailed description and the accompanying drawings are set forth only for purposes of illustrating the general principles of the invention and are not to be taken in a limiting sense.